Study On Aerodynamic Characteristics Of Maglev Transport System With A Low-Pressure Tube

Innovation is the soul of a nation's progress,and it is also the inexhaustible driving force for a country's prosperity.As for the field of rail transit,continuous technological innovations are the premise to ensure the favorable and sustainable development of the rail transit industry.Due to its network,large volume,safety,efficiency and other characteristics,the wheel-rail trains have great advantages in the field of medium and long distance,medium and high speed transportation.However,it is difficult to improve the operation speed of the wheel-rail train significantly,due to the inevitable limits,such as aerodymanic drag,wheel-rail adhesion,hunting instability,running noise and the limiting speed of pantograph-catenary.The maglev transport system with low-Pressure tube(LPT-MT system),which combines magnetic levitation technology with a low-pressure tube,can create a unique low-drag operation environment by using a closed low-pressure tube,making it possible for ?flying near-ground with 1000 km/h?.Theoretically,although the interaction between the air flow and the train will be reduced to some extent under the low-pressure envirionment,the ultra-high running speed of the train may bring some negetive effect.Aerodynamics is the primary problem for the research and development of LPT-MT system deemed as an ultra-high speed transport,and aerodynamic characteristics are closely related to the safety and stability of the train.Therefore,the flow field characteristics of the LPT-MT system were analyzed systematically in this paper,and the formula of aerodynamic drag of the train was conducted when it was running inside the low-pressure tube at a constant speed.It was found that the aerodynamic drag of the train running in the tube,is mainly related to the pressure in the tube,velocity and length of the train,block ratio,the equivalent surface roughness of the train and tube,the tube section forms and other parameters.Then,a three-dimensional,sutherland viscous,steady-state compressible N-S equation and a realizable k-? two equation turbulence model were used to numerically calculate the aerodynamic characteristics of the LPT-MT system in ANSYS FLUENT software.The aerodynamic drag of the maglev train under the condition of open air and low-pressure tube is studied,and the influence of block ratio,velocity of the train and tube pressure were analyzed as well.It turns out that the aerodynamic drag of the train mainly comes from the pressure drag between the head car and the tail car when the train is running in the open air condition,and the mid car mainly produce frictional drag.When the train speed reaches 980 km/h,the aerodynamic drag reaches 143.34 kN unexpectedly,which is about 6-7 times than the aerodynamic drag of high speed railway under 350 km/h.When the train is running in the low-pressure tube,the aerodynamic drag of the train is directly proportional to the square of the speed,and increases with the tube pressure linearly,and it also decreases with the decrease of the blocking ratio non-linearly.In addition,considering the energy consumption and traction power limit,the study shows that,if you want to achieve the target speed of 1000 km/h,the economical and reasonable block ratio should be about 0.32,and the tube pressure should be around 0.01 atm or even lower.In addition,the fourth chapter studies the influence of the train speed and tube pressure on the surface of the train and tube wall.It shows that the aerodynamic load increases with the train speed and tube pressure.When the train is running in the low-pressure tube,the load on the head car surface is very large,while the load on the mid car surface is relatively flat,and the load on the tail is small even less than the initial tube pressure.As for the aerodynamic load on the tube wall,they increased sharply in front of the train,and decreased in rear of the train,compared with the initial tube pressure,then,returned to initial tube pressure gradually after the fluctuated peak.Therefore,reducing the initial pressure in the tube and the speed of the train,can significantly decrease the aerodynamic load on the external surface of the train and the inner wall of tube.Finally,the fifth chapter studies the influence of different tube section forms and cross aisle on the aerodynamic drag of the train and aerodynamic load in the system.It was found that the aerodynamic loads on the inner tube wall are basically the same even under different tube sections forms,and the tube section forms has little influence on the aerodynamic load of the system,when the tube pressure is 0.01 atm and block ratio is 0.32.The aerodynamic drag of the train is the minimum when running in the rectangular tube.When the train speed is 0.8 Mach,the drag is 10.76 kN,which is basically the same as that running in the circular tube,and when the train is running in the archy tube,the aerodynamic drag is the maximum.In addition,by setting the cross aisle,the aerodynamic drag of the train can be reduced to some extent,and the aerodynamic load on the external surface of the head and the mid can be reduced,however,such effect is helpless on the tail.When the tube pressure is 0.01 atm and the block ratio is 0.32,the aerodynamic drag of the train in the tube with cross aisle can be reduced further to 9.877 kN,even the speed of the train is 0.8 Mach.In addition,setting cross aisle can reduce the the maximum aerodynamic load on the inner wall of the tube,but it also bring some pressure fluctuation at the location of cross aisle,and the fluctuation amplitude is smaller than the maximum aerodynamic load variation.